This invention relates to a circuit for switching the exposure factor of a camera.
Heretofore, the technique of switching the factor of exposure time (hereinafter referred to as "the exposure factor" when applicable) of an exposure time control circuit utilized a time constant circuit adapted to control the shutter control magnet by means of an integration voltage due to the collector current of a transistor. This was used together with a circuit adapted to apply a voltage across the base and emitter of the transistor. It is an arrangement in which in the circuit adapted to apply a voltage across the base and emitter of the transistor, a current flows in a variable resistor and the resistance of the variable resistor is changed, so that the voltage across the variable resistor is changed.
However, in using a variable resistor, the movable contact slides on the fixed resistance track, and therefore the contact resistance caused a problem. Furthermore, the resistance value may vary with time and temperature, and depending on its material.
In general, the exposure factors used with a camera are of the integer numbers (such as two (2) times, a half (1/2) time, etc.); that is, the values between such integer numbers are rarely used. Accordingly, in view of the construction of the variable resistor, the space for providing the intermediate resistances other than the set resistances is generally useless.